12) If a projectile is fired straight up at a speed of 10 m/s, the time it takes
ID: 2029627 • Letter: 1
Question
12) If a projectile is fired straight up at a speed of 10 m/s, the time it takes to reach the top of its path is 12) about A) 2 seconds. C) 10 seconds B) 1 second. D) not enough information to estimate 13) If an object moves with constant acceleration, its velocity must 13) A) change by the same amount each second B) change by varying amounts depending on its speed C) be constant also. D) always decrease. 14) 14) At one instant an object in free fall is moving downward at 50 meters per second. One second later its speed should be about E) 50 m/s A) 55 m/s. B) 100 m/s. C) 60 m/s. D) 25 m/s. 15) 15) An airplane that flies at 100 km/h in a 100-km/h crosswind has a ground speed of D) 100 km/h B) 141 km/h C) 0 km/h A) 200 km/h 16) 16) A pot falls from a ledge and hits the ground 45 m below. The speed with which it hits the ground is A) about 30 m/s. C) more than 120 m/s. B) about 120 m/s. D) about 60 m/s.Explanation / Answer
12)
initial speed u = 10 m/s
Time to reach the top is t = u / g
t = 10 / 10 = 1 s
Answer is B) 1 second
13)
Acceleration means change in velocity
Constant acceleration is constant change in velocity
Answer is A) Change by the same amount each second
14)
initial speed u = 50 m/s
time t = 1 s
from v = u + g*t
v = 50 + (10*1)
v = 60 m/s
Answer is C) 60 m/s
15)
Ground spped is 100 - (-100 = 200 km/s
Answer is A) 200 km/h
16)
h = 45 m
speed at the bottom is v = sqrt(2 * g * h)
v = sqrt(2 * 45 * 10) = 30 m/s
Answer is A) about 30 m/s
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